1. Field of Invention
The present invention relates to a post-processing treatment of low dielectric constant material. More particularly, the present invention relates to the post-processing treatment of low dielectric constant material through an ion implantation.
2. Description of Related Art
As soon as semiconductor fabrication reaches the 0.25 xcexcm line width stage, approximately 50% of transmission delay arc caused by resistance and capacitance (RC) along the metallic line that connects two transistors. Because delay between transistors is caused by the product of resistance (R) in the metallic line and capacitance (C) of the dielectric layer, there are two principle methods of reducing transmission D delay. The first method is to use a low resistance metal to fabricate the interconnection lines. The second method is to use a low dielectric constant material to insulate the metallic lines. To reduce resistance in metallic lines, copper (having resistivity of 1.7-xcexcxcexa9cm) is gradually replacing the metallic material aluminum (having resistivity of 2.7-xcexcxcexa9cm). To combat increased parasitic capacitance resulting from intensified narrow width effect, dielectric materials having a low dielectric constant arc needed.
Dielectric layers that are deposited in a later stage of semiconductor production usually demand high reliability, low stress, simplicity in manufacturing, low water absorption and case of integration with multiple conductive lines. In the past, most dielectric layers were formed by depositing silicon dioxide (SiO2) using a plasma-enhanced chemical vapor deposition (PECVD) process. The silicon dioxide layer so formed usually has a dielectric constant of around 3.9. Another type of commonly used dielectric material is a silicon dioxide based (SiO2-base) inorganic compound. The inorganic material generally has a dielectric constant greater than 3.0. However, as sub-micron devices are produced, the dielectric constant of the dielectric layer must be lowered correspondingly in order to back up the properties demanded. Otherwise, working speed of devices will be seriously affected, while power consumption and cross talk between neighboring devices will increase, as well.
Recently, a high molecular weight organic compound known as methylsesquioxane (MSQ) has been developed especially for forming dielectric layers. The MSQ compound can be spin-coated onto a substrate surface. FIG. 1A is a sketch showing a xe2x80x98cagexe2x80x99 structure of a portion of a MSQ molecule. FIG. 1B is a sketch showing a xe2x80x98netxe2x80x99 structure of a portion of a MSQ molecule. As shown in FIG. 1A and 1B, the compound MSQ is a silicon based (Si-base) substrate with methyl (CH3) radicals attached to the silicon atoms. Due to the presence of carbon, the MSQ compound has a porous structure. The porous structure makes the dielectric constant of a MSQ film rather low. In addition, of the high molecular weight organic dielectric materials, MSQ has relatively good heat stability. Since a MSQ dielectric layer is also relatively easy to form, the MSQ compound is likely to be widely used in the future.
However, the porous structure of MSQ compound may also lead to the absorption of moisture from the surrounding atmosphere. Since water is a polar material having a dielectric constant of about 78, the dielectric constant of an MSQ film may increase considerably when only a very small amount of moisture is absorbed. This water-absorption character also appears in other types of dielectric material having similar configuration such as hydrogen silsesquioxane (HSQ).
The present invention provides a post-processing treatment of a low dielectric constant material, which treatment is capable of reducing moisture absorption so that the low dielectric constant can be maintained. Consequently, a thin dielectric film of the low dielectric constant material can be used to insulate multiple conductive lines so that operating speed of integrated circuits is increased while power consumption of the circuits is reduced.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a post-processing treatment for a low dielectric constant material. The post-processing treatment includes a shallow implantation of the dielectric material to form a thin compact surface layer. This thin compact surface layer acts as a barrier preventing the absorption of moisture by the dielectric layer.
According to one embodiment of this invention, boron ions at an energy level of between about 10 and 50 keV and a dosage of between about 1xc3x971015 atm/cm2 and 1xc3x971016 atm/cm2 are used in the shallow implantation. Preferably, the energy level is 20 keV and the dosage level is 5xc3x971015 atm/cm2.
According to another embodiment of this invention, the post-processing treatment can be applied to an organic dielectric material layer such as a MSQ film or an inorganic dielectric material layer such as a HSQ film.
According to yet another embodiment of this invention, after the step of performing a shallow implantation of the low dielectric constant material, the treatment further includes performing an annealing operation for reducing the damages in the film structure caused by implanted ions.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.